Optical fiber primary coatings and fibers coated therewith

ABSTRACT

A curable thiol-ene composition specially adapted for use as a primary coating on optical fibers comprises a polythiol and a compound having a plurality of norbornene groups thereon, are characterized in that one of either the compound having the plurality of norbornene groups or the polythiol has a backbone of a poly(tetramethylene oxide), or is an oligomer thereof, and the poly(tetramethylene oxide) has a molecular weight of between 250 and 5,000. The formulations are relatively low viscosity liquids at practical application temperatures and cure substantially completely with very low irradiation fluence. The formulations cure in ambient air. There is no need to exclude oxygen or to control humidity. The formulations of the invention can be cured using low intensity UV lamps which do not generate significant amounts of heat. The cured products have excellent low temperature flexibility, good humidity and water absorbtion resistance and good thermal oxidative stability. The formulations may be applied to optical fibers using conventional techniques and cured with UV-vis or EB irradiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of applications, Ser. No.07/619,068, filed Nov. 28, 1990 and a continuation-in-part of Ser. No.08/056,128, filed Apr. 30, 1993, incorporated herein by reference, whichis a continuation-in-part of Ser. No. 07/746,649, filed Aug. 16, 1991,U.S. Pat. No. 5,208,281, incorporated herein by reference, which is acontinuation-in-part of Ser. No. 651,271, filed Feb. 5, 1991, U.S.5,167,882, incorporated herein by reference, which is acontinuation-in-part of Ser. No. 632,391, filed Dec. 21, 1990,abandoned.

TECHNICAL FIELD

This invention relates to a primary coating material for optical fibersand to optical fibers having primary coatings thereon.

BACKGROUND OF THE INVENTION

U.S. Pat No. 4,913,859 provides a general description of the manufactureof optical fiber as follows:

"In the manufacturing of optical fiber, a glass preform rod whichgenerally is manufactured in a separate process is suspended verticallyand moved into a furnace at a controlled rate. The preform softens inthe furnace and optical fiber is drawn freely from the molten end of thepreform rod by a capstan located at the base of a draw tower.

"Because the surface of the optical fiber is very susceptible to damagecaused by abrasion, it becomes necessary to coat the optical fiber,after it is drawn, but before it comes into contact with any surface.Inasmuch as the application of the coating material must not damage theglass surface, the coating material is applied in a liquid state. Onceapplied, the coating material must become solidified rapidly before theoptical fiber reaches a capstan. This may be accomplished byphotocuring, for example.

"Those optical fiber performance properties which are selected most bythe coating material are strength and transmission loss. Coating defectswhich may expose the optical fiber to subsequent damage arise primarilyfrom improper application of the coating material. Defects such as largebubbles or voids, non-concentric coatings with unacceptably thinregions, or intermittent coatings must be avoided. When it is realizedthat the coating thickness may be as much as the radius of an opticalfiber, it becomes apparent that non-concentricity can cause losses insplicing, for example.

"Transmission losses may occur in optical fibers because of a mechanismknown as microbending. Optical fibers are readily bent when subjected tomechanical stresses, such as those encountered during placement in acable or when the cabled fiber is exposed to varying temperatureenvironments or mechanical handling. If the stresses placed on the fiberresult in a random bending distortion of the fiber axis with periodiccomponents in the millimeter range, Light propagating in the fiber coremay escape therefrom. These losses, termed microbending losses, may bevery large. Accordingly, the fiber must be isolated from stresses whichcause microbending. The properties of the fiber coating play a majorrole in providing this isolation, with coating geometry, modulus andthermal expansion coefficient being the most important factors.

"Two types of coating materials are used to overcome this problem.Single coatings, employing a relatively high shear modulus, e.g. 10⁹ Pa,or an intermediate modulus, e.g. 10⁸ Pa, are used in applicationsrequiring high fiber strengths or in cables which employ buffer tubeswhere fiber sensitivity to microbending is not a significant problem.

"Dual coated optical fibers increasingly are being used to obtain designflexibility and improved performance. A reduction in the modulus of thecoating material reduces microbending sensitivity by relieving stresscaused in the fiber. Typically, an inner or primary coating layer thatcomprises a relatively low modulus material, e.g. 10⁵ -10⁷ Pa, isapplied to the optical fiber. The modulus of the primary coating shouldbe effective in promoting long bending periods for the fiber which areoutside the microbending range. Such a material reduces microbendinglosses associated with the cabling, installation or environmentalchanges during the service life of the optical fiber. In order to meettemperature conditions in expected areas of use, the low modulus coatingmaterial must be effective in the range of about -40° to 77° C. An outeror secondary coating layer comprising a relatively high modulus materialis applied over the primary layer. The outer coating layer is usually ofa higher modulus material to provide abrasion resistance and lowfriction for the fiber and the primary coating layer. The dual coatingserves to cushion the optical fiber by way of the primary layer and todistribute the imposed forces by way of the secondary layers, so as toisolate the optical fiber from bending moments."

"After the coating material or materials have been applied to the movingoptical fibers, the coating material or materials are cured, typicallyby exposure to ultraviolet radiation. In some coating systems, a primarycoating material is applied and cured by subjecting it to ultravioletenergy prior to the application of the secondary coating material."

Other references pertaining to coatings for optical fibers include: U.S.Pat. Nos. 4,125,859; 4,474,830; 4,935,455; 4,946,874; 4,956,198;4,973,611; 5,026,409; 5,139,872; 5,169,879; Martin, "Contribution ofDual UV Cured Coatings to Optical Fiber Strength and Durability,"Proceedings, Radcure Europe '87, pp 4-15-4-24 (May 1987); Chawala, etal, "An Infrared Study of Water Absorbtion of UV Curable Optical FiberCoatings," Radtech Report, 24-28January/February 1992; Smithgall, "ADynamic Modal for Optical-Fiber Coating Application," J. LightwaveTechnology, 8, 1584-1590 (October 1990); Simoff et al, "Thermo-OxidativeAging of a Primary Lightguide Coating in Films and Dual-Coated Fibers,"Polymer Engineering and Science, 29, 1177-1181 (Mid-September 1989); andOverton et al, "Time Temperature Dependence of Dual Coated LightguidePullout Measurements," Polymer Engineering and Science, 29, 1169-1171(Mid-September 1989).

In U.S. Pat. No. 5,171,609 there is described a common problemencountered in curing of optical fiber coatings, that being the tendencyof heat from high energy UV lamps typically employed to cure the coatingmaterial to evaporate some coating from the fiber and to deposit same onthe wall of the transparent curing chamber, thereby darkening thechamber and reducing energy available to cure the coating. Variousmechanical solutions to this problem have been proposed but all arecomplicated and cumbersome.

SUMMARY OF THE INVENTION

The invention hereof pertains in one aspect to thiol-ene formulationsbased on norbornene functional polyenes which are uniquely suited foroptical fiber primary coatings. The formulations are easily applied,relatively low viscosity, liquids at practical application temperaturesand cure substantially completely with very low irradiation fluence. Theformulations cure in ambient air. There is no need to exclude oxygen orto control humidity, as is the case with some prior art compositions.The formulations of the invention can be cured using low intensity UVlamps which do not generate significant amounts of heat and therefore donot require special apparatus to avoid evaporation/condensation transferof coating material from the fiber to the light source window. The curedproducts have excellent low temperature flexibility, good humidity andwater absorbtion resistance and good thermal oxidative stability. Thecompositions are characterized by use of a norbornene functional polyeneor a polythiol which has a poly(tetramethylene oxide) backbone with amolecular weight in the range of about 250 to about 5000. In preferredcompositions the polythiol component and the norbornene functionalcomponents are fully miscible, suitably by using an oligomeric form ofone or the other of the two components.

Cured polymers prepared from the compositions of the invention; opticalfibers coated therewith; and methods of preparing such coated fibers byapplying the composition as a liquid and then irradiating the coatingwith UV-vis or EB radiation comprise further aspects of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an end cross sectional view of an optical fiber which includesprimary and secondary protective coating layers.

FIG. 2 is a plot of fractional conversion against fluence of UVirradiation comparing cure response of a formulation of the inventionwith a norbornene-thiol formulation based on a prior art norborneneresin.

DETAILED DESCRIPTION OF THE INVENTION

One type of known apparatus which may be used to draw and coat anoptical fiber is described and illustrated in U.S. Pat. No. 4,913,859,incorporated herein by reference. The coatings are suitably cured byUV-vis or EB (electron beam) irradiation.

As mentioned hereinbefore, it is frequently common place to apply dualcoatings to a drawn optical fiber. These provide protection for theoptical fiber, as well as render the optical fiber more flexible thanwith a single coating layer. A coated optical fiber 10, comprisingoptical glass fiber 12, a primary coating 14 adjacent the optical glassfiber and a secondary coating layer 16 overlying the primary coating, isshown in FIG. 1. The present invention pertains to formulations for theprimary coating.

The primary coating formulations of the invention are a species ofthiol-ene composition, comprising a polyene, a polythiol and aphotoinitiator.

The polyenes used in the formulations of the invention are suitablydinorbornene terminated poly(tetramethylene oxide) polymers (also knownas poly(TMO) or poly THF). In accordance with convention, molecularweight of the polyether backbone is included in the name of thecompound, i.e. hydroxyl terminated poly(tetramethylene oxide 650) [pTMO650] has an average molecular weight, based on hydroxyl numbercalculation, of approximately 650. These polyether backbones have beenfound to provide an especially good combination of low Tg, moistureresistance, low composition viscosity and other desired properties whilethe thiol-norbornene system provides an especially fast cure. Polyetherbackbones having molecular weights in the range of 250 to as high as5000 are suitable, depending on coating application temperature, withmolecular weights in the range of 650-2000 being preferred. Mostpreferably, the molecular weight of the backbone is in the range of650-1000, as higher molecular weight materials give formulations whichare waxy solids at ambient temperature and must be mildly heated inorder to be applied.

The norbornene termination of the polyether backbone can be obtained ina variety of ways. Conveniently, hydroxy terminated poly(tetramethyleneoxide) can be reacted with hydroxy reactive norbornene functionalcompounds such as acid chlorides, isocyanates, azlactones andchloroformates. The choice of linkage does influence the propertiesobtained but generally not so much as the backbone polyether. Examplesof suitable polyethers include the following: ##STR1##Poly(tetramethylene oxide) di-[(norborn-5-ene-2-)methylcarbonate],##STR2## Poly(tetramethylene oxide) di-(norborn-2-ene-5-carboxylate),##STR3## Poly(tetramethylene oxide) di-(norborn-2-ene-5-carbamate) and##STR4## Poly(tetramethylene oxide)di-[2-(norborn-2-ene-5-carboxamido)-2,2-dimethylacetate]. Suitably, n isan integer of 1-30.

The polythiol component of the inventive compositions may be derivedfrom any compound having an average of more than two thiol groups permolecule. Compatability with the norbornene functional polyether,however, is important in order to maintain shelf stability of theformulation. Generally trithiol functional compounds, such astrimethylolethane tris-mercaptopropionate, trimethylolpropanetris-mercaptopropionate ([TMP]2), trimethylolethanetris-mercaptoacetate, and trimethylolpropane tris-mercaptoacetate, willbe fully miscible with the norbornene compound and can be used as is.

It has been found that polythiols obtained by esterification of a tetraor higher functionality polyol with an α or β-mercaptocarboxylic acidsuch as thioglycolic acid, or β-mercaptopropionic acid, especiallypentaerythritol tetramercaptoacetate and pentaerythritoltetrakis-β-mercaptopropionate (PETMP)., do not always give fullymiscible formulations with the result that they sediment on standing andmust be throughly remixed to disperse prior to use. This is notdesireable for many commercial applications, including high volumeoptical fiber primary coating applications.

Formulations derived from tetra and higher polythiols, however can beeasily employed without the need for remixing at the time of use if thetetra or higher functional polythiol compound is first reacted with astoichiometric deficiency of a poly(tetramethylene oxide) dinorbornenecompound to provide a polythiol terminated oligomer which is thenblended with an additional amount of a poly(tetramethylene oxide)dinorbornene compound (which may be the same or different as thecompound used to make the polythiol prepolymer) to form the thiolenecomposition. Suitably, the thiol functionalized poly(TMO) dinorborneneoligomer may be prepared by pre-reacting 1.0 equivalent of PETMP withabout 0.3 equivalents of the poly(TMO) dinorbornene monomer. Theoligomer is obtained as a solution in PETMP. The new thiol oligomersolution is miscible with the poly(TMO) dinorbornene monomer atequivalent concentrations. Although the viscosity of the modifiedformulation is higher than the corresponding unmodified blend, the newcompositions are clear and homogeneous. The new oligomer assists thesolubility of PETMP in the poly(TMO)-norbornene monomer. Sedimentationis not observed on dark storage at ambient temperature over a 24 hourperiod.

The method used to produce the new monomer is straightforward, fast andrequires no additional materials nor special lab equipment. Theprocedure used is illustrated below in Example 12.

Alternative formulations within the scope of the invention employ adithiol having a poly(tetramethylene oxide) backbone and a pluralnorbornene compound having three or more norbornene groups per molecule.For instance, formulations based on pentaerythritol tetrakis-(norbornenecarboxylate), or trimethylpropane tri-(norbornene carboxylate), andpoly(tetramethylene oxide)(1000) dimercaptopropionate, will give curedproperties similar to the di-poly(TMO)norbornene carboxylate/PETMP or[TMP]2 formulations exemplified herein.

The ratio of the polyene to the polythiol component can be varied withina range of ene to thiol groups of from about 1.0:0.8 to about 1.0:1.3.Thiol content below about 1.0:0.8, ene/thiol, in the formulation may notgive a composition cureable with the desired low energy input. Thiolcontent above a ratio of 1.0:1.3, ene/thiol, possibly as high as 1.0:1.5may be satisfactory in some instances. Generally it is preferred thatthe ratio of ene to thiol groups be 1:1.

While a curable composition using norbornene functional compounds of theinvention may include both difunctional norbornenyl compounds anddifunctional thiol compounds, it will be understood that at least aportion of at least one of these components should contain more than twofunctional groups per molecule to produce a crosslinked product whencured. That is, the total of the average number of norbornene groups permolecule of norbornene functional compound and the average number ofcoreactive thiol groups per molecule of the thiol functional compoundshould be greater than 4 when a crosslinked cured product is desired.This total is referred to as the "total reactive functionality" of thecomposition.

Compositions formulated for electron beam (EB) curing do not require acure initiator. Compositions formulated for UV-vis or thermal cure willdesireably include a photoinitiator or thermal initiator, respectively.The initiator may be radical or cationic. Most suitably it is a freeradical photoinitiator. Examples of free radical photoinitiators includebenzoin and substituted benzoin compounds, benzophenone, Michler'sketone, dialkoxybenzophenones, dialkoxyacetophenones, peroxyestersdescribed in U.S. Pat. Nos. 4,616,826 and 4,604,295, etc. Thephotoinitiator is employed in an amount effective for initiating cure ofthe formulation, typically 0.5-5%. Combinations of two or morephotoinitiators may also be employed, for instance to optimize responsefor a particular UV-vis energy source.

The formulations also preferably include a stabilizer. Preferredstabilizers, described in EP 428,342 incorporated herein by reference,are non-acidic nitroso compounds, particularlyN-nitrosohydroxylarylamines and salts thereof. A suitable such compoundis the aluminum salt of N-nitrosophenylhydroxylamine (Q1301™, Wako PureChemical Industries, Richmond, Va.) which may be usefully employed atlevels between about 10 ppm and 1%, preferably 100-10,000 ppm.

The thiol-ene formulations which employ norbornene functional polyenes,even with stabilization, are quite sensitive to fluorescent light andmay need to be kept in the dark to remain stable for more than a fewdays. If storage for periods of more than a few months is necessary,separating norbornene and thiol compounds in a two-part formulation maybe desireable.

As described in copending parent application, Ser. No. 08/056,128, filedApr. 30, 1993, purification of the norbornene resin by contacting itwith an amphoteric treating agent selected from the group consisting ofsilicated magnesium oxide, basic aluminum oxide, silica gel, magnesiumoxide, magnesium hydroxide, calcium oxide, calcium hydroxide, bariumoxide, and barium hydroxide, and then separating the resin from thetreating agent prior to mixture with the polythiol significantlyimproves the shelf life of the thiol-ene formulation formed therefrom.As described in the application of David M. Glaser, Anthony F. Jacobineand Paul Grabek, Ser. No. 08/081,078, filed concurrently herewith,entitled "Thiol-Ene Compositions With Improved Cure Speed Retention,incorporated herein by reference, similar treatment of the polythiolcomponent may also be desirable to stabilize the cure speed performanceof the composition on aging and to further stabilize the shelf-life ofthe formulation.

As described in U.S. Pat. No. 5,208,281, triiodide and other polyiodideshave also been found useful shelf-life stabilizers for thiol-eneformulations based on norbornene resins. Suitable polyiodide stabilizersmay be KI/I₂ (1:2 parts by wt) solutions in water at levels providing10-2,000 ppm I₂, preferably 30-800 ppm I₂. An aqueous KI/I₂ solution inwhich the concentration of I₂ is 1N is a suitable such solution.Compatible organic solvents such as lower alcohols may also be employedto introduce a polyiodide stabilizer into the formulation. The Ki/I₂solution is suitably added to either the norbornene resin or the thiolresin prior to mixing.

Alternatively, as described in the application of David M. Glaser,Anthony F. Jacobine and Paul J. Grabek, entitled "Stabilizer System forThiol-Ene Compositions," Ser. No. 08/081,456 filed concurrentlyherewith, the formulation may be stabilized with a stabilizer systemcomprising an alkenyl substituted phenolic compound and one or morecompounds selected from the group consisting of a free radicalscavenger, a hindered phenolic antioxidant and a hydroxylaminederivative. Examples of suitable alkenyl substituted phenolic compoundsinclude 2-propenylphenol, 4-acetoxy styrene, 2-allylphenol, isoeugenol,2-ethoxy-5-propenylphenol, 2-allyl-4-methyl-6-t-butylphenol,2-propenyl-4,-methyl-6-t-butlyphenol, 2-allyl-4,6-di-t-butylphenol,2-propenyl-4,6-di-t-butylphenol and 2,2'-diallyl-bisphenol A, suitablyat levels of 500 ppm-5000 ppm by weight of the composition. Preferablythe alkenyl phenolic compound is used with a N-nitrosoarylhydroxylaminesalt, a radical scavenger such as p-methoxy phenol (MEHQ), and ahindered phenolic antioxidant such as butylated hydroxy toluene (BHT).

The formulations of the invention are characterized by very lowviscosities for low Tg organic polymer forming compositions.Formulations employing poly(tetramethylene oxide) backbones of 1000 MWor less are liquids at ambient temperature with typical 25° C.viscosities of 2000 mPas or less. Using trithiols, clear homeogeneousliquid formulations can be readily prepared having viscosities below1000 mPas or less.

Glass transition temperatures of the cured polymers are very low, nomore than -10° C., typically less than -20° C. and in the preferredformulations less than -35° C. Cured polymers whose Tg is below -50° C.can be readily produced, as illustrated in examples 14 and 18-21.

To strengthen adhesion in the interface between the glass fiber and thecoating material it is recommended that an adhesion promoter also beemployed in the formulation. Suitable adhesion promoters which may beemployed are identified in U.S. Pat. No. 5,028,661, incorporated hereinby reference, and various other organic acid and silane compounds knownto be useful for promoting adhesion, especially to glass. Examples ofadhesion promoters include acrylic and norbornene acid phosphate esters;itaconic, acrylic and methacrylic acids; maleic, fumaric and norbornenedicarboxylic acids and their half esters; and, especially, thiol, epoxy,norbornene, acrylic or methacrylic functional silane compounds havingtwo or three hydrolyzable groups bound to silicon. Examples of suchsilane compounds include 3-methacryloxypropyl trimethoxysilane,mercaptopropyl trimethoxysilane, glycidoxypropyl trimethoxysilane, andthe like. The adhesion promoters are employed at conventional levels,suitably about 0.1-3.0 percent by weight of the formulation.

The invention may be illustrated by the following nonlimiting examples.

EXAMPLE 1

Synthesis of endo, exo-Norborn-2-ene-5-carbonyl Chloride, I

In a 1000 ml four-necked, round-bottomed flask that was equipped with amagnetic stirrer, an efficient condenser, a constant pressure additionfunnel, and a thermometer that was connected to a Thermowatch™thermostatic controller was stirred acryloyl chloride (271.8 g, 3.00mol) under a nitrogen atmosphere. Freshly cracked and distilledcyclopentadiene monomer (198.2 g, 3.00 mol) was added at such a ratethat the reaction temperature did not exceed 80°-90° C. at any timeduring the addition. When the addition was completed the reaction wasstirred for an additional three hours. Residual starting materials wereremoved using a water aspirator and the crude reaction mixture was thendistilled in vacuo to give the purified product (b.p. 66°-70° C. at 4mmHg).

EXAMPLE 2

Synthesis of endo, exo-Norborn-2-ene-5-methyl-5-carbonyl Chloride, II

In a 1000 ml four-necked, round-bottomed flask that was equipped with amagnetic stirrer, an efficient condenser, a constant pressure additionfunnel, and a thermometer that was connected to a Thermowatch™thermostatic controller was stirred freshly distilled methacryloylchloride (250 g, 2.391 tool, Aldrich Chemical Co.) under a nitrogenatmosphere. Freshly cracked and distilled cyclopentadiene monomer(173.62 g, 2.63 mol) was added at such a rate that the reactiontemperature did not exceed 80°-90° C. at any time during the addition.When the addition was completed the reaction was stirred for anadditional three hours. Residual starting materials were removed using awater aspirator and the crude reaction mixture was then distilled invacuo to give the purified product (b.p. 74°-76° C. at 4-7 mm Hg).

EXAMPLE 3

Synthesis of endo, exo-Norborn-2-ene-5-isocyanate, III

Sodium azide (228.47 g, 3,51 tool in 250 ml deionized water) was addeddropwise to a stirred solution of norborn-2-ene-5-carbonyl chloride (500g., 3.19 mol) and tetra-(n-butyl)ammonium bromide (2.5 g, 0.0077 tool)in dichloromethane (1000 ml) in a 4 liter beaker which had been cooledto 5°-10° C. and maintained at this temperature throughout the reaction.After the addition was completed, the organic layer was separated anddried over anhydrous sodium sulfate and filtered. The filtered solutionwas then added dropwise to a 2 L round-bottomed flask that was set upfor distillation containing benzene (500 ml) maintained at 70° C.Dichloromethane was removed by distillation (overhead temperature50°-55° C.) and collected. After the addition was completed thetemperature of the reaction mixture was maintained at 70° C. for twohours, The reaction mixture was then concentrat on a rotary evaporatorand distilled in vacuo. The purified product was collected as a fractionb.p. 60°-65° C. at 115 mm Hg.

EXAMPLE 4

Synthesis of endo, exo-2-(Norborn-5-ene-5)-4,4-dimethyloxazoline-5-oneNorbornene Azlaetone (NAz), IV

In a 1000 ml four-necked, round-bottomed flask that was equipped with amagnetic stirrer, an efficient condenser, a constant pressure additionfunnel, and a thermometer was stirred2-vinyl-4,4-dimethyloxazoline-5-one (501.66 g, 3.61 mol, SNPE, Inc.,Princeton, N.J.) under a nitrogen atmosphere. The solution wasthermostated at 40° C. by means of a Thermowatch™ Controller and freshlycracked and distilled cyclopentadiene monomer (262.3 g, 3.97 mol) wasadded at such a rate that the reaction temperature did not exceed90°-100° C. over the course of the addition. When the addition wascompleted the reaction was aged at 95° C. for two hours and thenconcentrated on a rotary evaporator to remove excess cyclopentadienemonomer. The crude mixture was distilled in vacuo (b.p. 70°-73° C. at0.2 mm Hg) to yield the purified product (yield 689.7 g, 93% Th.) as acolorless liquid that rapidly solidified at room temperature. High fieldNMR analysis (300 MHz) indicated that the distillate was a mixture ofendo and exo isomers of the desired product and was essentially pure,

EXAMPLE 5

Synthesis of Norborn-5-ene-2-methyl Chloroformate, V

Norborn-5-ene-2-methanol (196.20 g, 1.58 mol, Aldrich Chemical Co.) wasstirred in toluene (250 ml) in a 1000 ml three-necked, round-bottomedflask that was equipped with a magnetic stirrer, a dry ice condenser, aconstant pressure addition funnel, and a thermometer. The reaction wascarried out under a nitrogen atmosphere and the outlet of the bubbletube was vented into a dilute solution of sodium hydroxide. The solutionwas cooled to around 10° C. and a solution of phosgene (171.9 g, 1.738mol) in toluene (250 ml) was added dropwise at such a rate that thereaction temperature did not exceed 25° C. at any time. When theaddition was completed the reaction was warmed to room temperature andstirred for sixteen hours. Excess phosgene was removed by a subsurfacenitrogen sparge at 30° C. for three hours. Excess solvent was removed ona rotary evaporator and the purified product was obtained by flashvacuum distillation (oil temperature 150° C., b.p. 75°-80° C. at 1.5 mmHg).

EXAMPLE 6

Synthesis of Poly(tetramethylene oxide 650) Di-(Norborn-5-ene-2-)methylCarbonate, VI

Hydroxy terminated poly(tetramethylene ether 650) (232.91 g, 0.719 eq.OH) and pyridine (64.3 g, 0.814 mol) was stirred in toluene (300 ml)under a nitrogen atmosphere in a 1000 ml four-necked, round-bottomedflask equipped with mechanical stirring, a thermometer and a constantpressure addition funnel containing norborn-5-ene-2-methyl chloroformate(150 g, 0.74 mol). The chloroformate was added dropwise at such a ratethat the reaction temperature slowly climbed to 60° C. during theaddition. When the addition was completed the reaction mixture was agedat 70° C. for three hours at which point methanol (5.0 g, 0.16 mol) wasadded to the reaction mixture. The reaction mixture was filtered throughCelite™ diatomaceous earth and the filtrate was concentrated on a rotaryevaporator to remove solvent. The crude yellow oil was then passedthrough a two inch wiped film evaporator at 125° C. and 0.3 mm Hg. Theyield of product was 328 g.

EXAMPLE 7

Synthesis of Poly(tetramethylene oxide 650)Di-(Norborn-2-ene-5-Carboxylate), VII

Hydroxy terminated poly(tetramethylene oxide 650, Poly(TMO) (401.94 g,1.241 eq. OH, BASF Corporation, Parsippany, N.J.) and pyridine (111.06g, 1.41 mol) was stirred in toluene (400 ml) under a nitrogen atmospherein a 2000 ml four-necked, round-bottomed flask equipped with mechanicalstirring, a thermometer and a constant pressure addition funnelcontaining norborn-2-ene-5-carbonyl chloride (200 g, 1.278 mol). Theacid chloride was added dropwise at such a rate that the reactiontemperature slowly climbed to 70° C. during the addition. When theaddition was completed the reaction mixture was aged at 70° C. for threehours at which point methanol (5.0 g, 0.16 mol) was added to thereaction mixture. The reaction mixture was filtered through Celite™diatomaceous earth and the filtrate was concentrated on a rotaryevaporator to remove solvent. The crude oil was then passed through atwo inch wiped film evaporator at 125° C. and 0.4 mm Hg. The yield ofproduct was 535 g (96.5% Th.).

EXAMPLE 8

Synthesis of Poly(tetramethylene oxide 650)Di-(Norborn-2-ene-5-Carbamate), VIII

Hydroxy terminated poly(tetramethylene oxide 650) (174.74 g) was stirredunder a nitrogen atmosphere with diazabicycloundecane (0.5 g) in a 500ml four-necked, round-bottomed flask equipped with mechanical stirring,a thermometer, and a constant pressure addition funnel containingnorborn-2-ene-5-isocyanate (75 g, 0.556 mol). The addition of isocyanatewas controlled at such a rate that the reaction temperature did notexceed 35° C. during the addition period. The reaction mixture was thenheated to 70° C. and held at that temperature for six hours. Wheninfrared spectroscopic analysis showed no further change in the NCOband, the reaction mixture was cooled and the crude oil was then passedthrough a two inch wiped film evaporator at 125° C. and 0.4 mm Hg. Theyield of crude oil was 243.3 g.

EXAMPLE 9

Synthesis of Poly(tetramethylene oxide 650)Di-[2-(Norborn-2-ene-5-Carboxamido)-2,2-Dimethylacetate], IX

A mixture of 2-(Norborn-2-ene-5)-4,4-dimethyloxazolin-5-one (130.36 g,0.636 mol), hydroxy terminated poly(tetramethylene oxide 650) (200 g)and diazabicycloundecane (3.31 g) was stirred under a nitrogenatmosphere in a 1000 ml four-necked, round-bottomed flask equipped withmechanical stirring, and efficient condenser and a thermometer. Thereaction mixture was heated to 100° C. After eight hours infraredspectroscopy indicated that the distinctive azlactone carbonyl band at1817 cm⁻¹ had completely disappeared. The crude product was then passedthrough a two inch wiped film evaporator at 125° C. and 0.4 mm Hg. Theyield of viscous oil was 314.8 g.

EXAMPLE 10

Mechanical Properties of Norbornene-Thiol Copolymers

Curable compositions were prepared by mixing equivalent amounts ofnorbornene functional resins with PETMP and photoinitiator (DAROCUR®1173, sold by EM Industries, Hawthorne, N.Y.). Specimens for mechanicaltesting were cured on a Fusion™ System conveyerized dual lamp system(two D bulbs). Tensile properties were determined on an Instron™Universal Testing Machine Model 4505 using 20 mil films according to amodified ASTM D-883 test. Dynamic mechanical tests were carried out on aRheometrics Dynamic Analyzer RDA II with torsion rectangular geometry.Strain sweeps were carried out on duplicate samples to insure thattemperature sweeps were carried out in the linear response region.Results of testing several formulations using several norborneneterminated poly(tetramethylene oxide) polyenes are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Properties of Norbornene Capped Tetramethylene Oxide/PETMP                    Formulations For Fiber Optic Coatings                                                 Poly(TMO)                                                                            Poly(TMO)                                                                            Poly(TMO)                                                                            Poly(TMO)                                                                             Poly(TMO)                                                                            Blend                             Property                                                                              2900 Naz*(A)                                                                         1000 Naz(B)                                                                          2000 Naz(C)                                                                          1000 Est**(D)                                                                         2900 Est(E)                                                                          (F)                               __________________________________________________________________________    E.sub.30%                                                                             428    483    388    248     438    358                               % ε.sub.break                                                                 58      32     44     25     76     38                                OIT***  221    190    157    201     238.3  212                               TGA.sub.200° C. ****                                                           OK     OK     OK     OK      OK     OK                                Tg      -64.4  --     --     -49     --     -61.6                             H.sub.2 O Uptake                                                                      0.3, -0.42                                                                           1.60, 2.0                                                                            1.7, 0.92                                                                            0.5, -0.2                                                                             0.63, -0.1                                                                           -0.43                             __________________________________________________________________________     *Naz = Norbornenylazlactone terminated poly(TMO).                             **Est = Norbornenecarboxylate (ester) Terminated poly(TMO).                   ***OIT is the oxidation induction temperature of a sample heated at           10° C. per minute under oxygen.                                        ****TGA results are based on isothermal runs carried out at 200° C     for 40 minutes.                                                          

EXAMPLE 11

Endgroup Effects

The effect of various end groups on a single oligomeric backbone(poly[TMO 650]) was also investigated. Table 2 outlines the mechanicalproperties and glass transition temperatures of these materials. It isseen that in poly(TMO (650) based systems, the identity of the endgroupsdoes not wield significant influence on final mechanical and thermalproperties. Rather, the flexibility of the Poly(TMO) (650) backboneexerts the major influence on the properties of the cured filmregardless of the end group and produces a material which is rubbery atroom temperature.

                  TABLE 2                                                         ______________________________________                                        Tensile Properties and Glass Transition Temperatures of Various               Norbornene-Functionalized Poly(TMO 650) Resin                                            Tensile   Tensile   Elongation                                     N-Functionality                                                                          Modulus   Strength  at Break                                                                              Tg                                     (w PETMP)  (MPa)     (MPa)     (%)     (°C.)                           ______________________________________                                        VI         4.70 ± 0.23                                                                          0.69 ± 0.05                                                                          17.3 ± 2.0                                                                         -39.0                                  (Norbornene-                                                                  methyl Carbonate                                                              Ester)                                                                        VII        5.62 ± 1.03                                                                          0.81 ± 0.11                                                                          16.7    -39.0                                  (Norbornene                                                                   Ester)                                                                        VIII       5.86 ± 0.28                                                                          1.17 ± 0.25                                                                          25.0 ± 6.6                                                                         -16.0                                  (Norbornene                                                                   Urethane)                                                                     IX         1.38 ± 0.28                                                                          0.53 ± 0.06                                                                          51.5 ± 7.7                                                                         -20.0                                  (Norbornene-                                                                  amido Dimethyl-                                                               acetate)                                                                      ______________________________________                                    

The effect of polar functional groups on Tg in the same oligomericseries is confirmed. Comparison of Tg values for IX (amide functional)and VIII (urethane functionality) with VI (carbonate ester) and VII(carboxylate ester) show stiffening due to restricted rotation of theamide and urethane groups and hydrogen bond formation. The Tg values forthe former materials exceed the latter by approximately 20°-25° C., butstill are well below published specifications for maximum desireable Tgfor optical fiber primary coating materials.

EXAMPLE 12

Procedure for preparation of prereacted poly(TMO) thiol monomer andformulation of thiol-ene compositions.

Poly(TMO) dinorborene (17.93 g, 0.015 moles) and pentaerythritoltetra-(3-mercaptopropionate) (PETMP) (W. R. Grace; 12.20 g, 0.025 moles)were placed in a 250 ml round bottomed glass reaction flask equippedwith an efficient mechanical stirrer and a liquid addition funnel. Themixture was stirred to provide a uniform emulsion of the two comonomers.A small aliquot was removed for IR spectral analysis. 2,2'-Azobis(2methylbutanenitrile) (Vazo 67, DuPont; 0.041 g; 2.14×10⁻⁴ moles) wasadded to the cloudy blend and the mixture was stirred and heated to anexternal oil-bath temperature of 85° C. over a period of 30 minutes.During this time the mixture clarified and became more viscous. Heatingand stirring was continued for an additional 30 minutes. During thistime another small aliquot was removed for IR analysis, which indicatedcomplete consumption of the norbornene monomer. This new composition maybe regarded as a mixture of higher functionalized thiol oligomersbearing poly(TMO)-norbornane backbones and tetra thiol PETMP.

The reaction mixture was cooled to ambient temperature and 1.68 g of asolution of a 20:1 premixture of DAROCUR 1173 and Q1301 was added to thestirred mixture along with an additional quantity of poly(TMO)dinorbornene (53.77 g, 0.045 moles). This part of the procedure wasconducted under yellow lighting. The mixture was stirred for about 30minutes and removed from the reaction flask. The product obtained isreferred to as Formulation A and contains 20% excess norbornene monomerover the amount required for equivalent stoichiometry with thiol.

A stoichiometric equivalent composition was prepared by adding 0.30 gPETMP (0.6 m moles) to 10 g of Formulation A (3.0 m moles thiol; 7.2mmoles dinorbornene). This product is referred to as Formulation B.

Both formulations were stored in the dark at ambient temperature for 24hours. After this time both were, surprisingly, found to be clear andhomogeneous. By comparison, a stoichiometric blend of PETMP andpoly(TMO) dinorbornene, which had not been prereacted, was cloudy andhad begun to separate into two phases. The new prereacted thiolterminated oligomers assist the miscibility of PETMP in poly(TMO)dinorbornene resins and permit the formulation of homogeneous singlepart products to be made from otherwise incompatible comonomercomponents.

The formulated products, A and B, were found to be highly sensitive toUV light. Both compositions fixtured glass slides in less than 1 secondirradiation from a "Blak-Ray" lamp. A thin film of formulation A curedto give a tacky coating after 5 seconds UV exposure, whereas formulationB gave a tack-free film after a similar exposure.

The initial IR spectrum of the reaction product showed absorption peaksat 715 cm⁻¹ and at 2570 cm⁻¹ characteristic of the norbornene and thiolmonomers, respectively.

The IR spectrum of the reaction product after heating gave absorbancevalues corresponding to a complete consumption of the norbornene monomerand 38% conversion of thiol. Since these values are close to those thatwould be expected from the complete reaction of the norbornene-(TMO)monomer with 2 equivalents of thiol (30% equivalents of norbornene inoriginal mixture), the predominant molecular species of the prereactedpolymer may be regarded as a hexafunctional thiol terminatedpoly(TMO)-dinorbornane having the structure: ##STR5##

EXAMPLE 13

Photosensitivity and Degree of Cure of Poly(TMO) Dinorbornene-PETMPResins Compositions.

The coating of optical fibers with UV curable compositions is performedin a continuous high speed process, frequently at speeds in the regionof 10 m/sec. To be useful the primary coating composition must combinehigh photosensitivity in the uncured state and flexibility in the curedstate. These characteristics tend to be mutually exclusive and aredifficult to obtain. This experiment is designed to measure thephotosensitive response of the poly(TMO) dinorbornene-thiol to UV lightand to estimate the final extent of cure in the irradiated product. Itis also an objective of the experiment to compare the performance of thenew poly(TMO) resins with the prior art norbornene-thiol compositions.

A coating composition was prepared, under yellow lights, by blendingtogether, in a mechanical mixer, the following materials:

    ______________________________________                                        poly(TMO 1000) dinorbornene carboxylate (eq. wt.                                                          12.783 g                                          639)                                                                          PETMP (eq. wt. 122)         2.459 g                                           2-hydroxy-2-methyl-1-phenylpropan-1-one                                                                   0.292 g                                           (DAROCUR 1173, photoinitiator, EM Industries)                                 aluminum tris-N-nitrosophenylhydroxylamine (Q1301                                                         0.015 g                                           thermal stabilizer, Wako)                                                     ______________________________________                                    

The ratio of norbornene and thiol comonomers represent equivalentstoichiometry.

The blended product was obtained as a cloudy mixture owing to theincomplete miscibility of the norbornene and thiol components, as notedin the previous example. However, since bulk phase separation did notoccur for several hours after mixing, it was possible to carry out thephotochemical evaluation without the need to employ the prereactedresin.

To measure the photochemical response of the composition, a small samplewas smeared onto a potassium bromide disc to give a uniform thin film ofthe product. The coated KBr plates were exposed to UV light from a highpressure short arc 500 W mercury lamp illuminator supplied by OrielCorporation. Infrared radiation was removed by reflecting the beam froma 290-390 nm dichroic mirror. The UV light was focused through anoptical integrator, collimating quartz lens and a narrow 365 nm bandpassfilter (03 FIM 028, Melles Griot) onto to the coated KBr plate. Thisarrangement produces a 10 nm wide band of UV light, centered at 365 nm.The collimating lens ensures a uniform distribution of light intensityover the width of the salt plate. The dichroic mirror ensures thatcuring takes place at ambient temperature, even after long exposures. Anelectronically activated shutter, located directly after the opticalintegrator, was used to control the exposure time in 100 ms timeintervals with a shutter open/close time of 20 ms.

The salt plates were placed directly below the bandpass filter in ananti reflective chamber to minimize possible errors due to reflected UVlight. The incident radiant power (irradiance) was determined at thesame position as the sample, prior to each experiment, using acalibrated radiometer (IL 1700) and detector (SED400), supplied byInternational Light Inc. The detector was equipped with a filter set,optimized for maximum sensitivity at 365 nm. Fluence (incident energyper unit area) was calculated from the product of irradiance andexposure time.

The norbornene/thiol polymerization reaction was followed by measuringabsorbance changes in the infrared spectrum at 715 cm⁻¹. This peak,characteristic of the C--H asymmetric deformation of cis-alkenes is freeof interference bands and is relatively intense compared to the S--H andC═C stretching vibrations. On prolonged UV exposure, the absorbancedisappears completely. Absorbances were measured by standard base-linetechniques and errors due to slight changes in film thickness wereeliminated by measuring an absorbance ratio to an internal standardunaffected by UV exposure. Ratios were found to be constant over a rangeof film thickness, provided that the peak values were below about 1.0absorbance units.

Assuming a linear relationship of absorbance with concentration, asdefined by the Beer-Lambert law, the fractional conversion of enemonomer (F) is given by the equation:

    F=1-Rt/Ro

where Ro and Rt are the absorbance ratios before and after UV exposurerespectively.

The infrared analysis was carried out directly following irradiation andperformed on a Nicolet 205 FT IR spectrometer collecting 32scans/spectrum at a resolution of 4 cm⁻¹. A separate sample film wasprepared for each exposure time. The UV irradiance was 1.26 mW/cm².

The results obtained from this experiment are listed in Table 3.

                  TABLE 3                                                         ______________________________________                                        Exposure Time                                                                             Fluence                                                           (s)         (mJ/cm2)      Rt/Ro   F                                           ______________________________________                                        0           0             0.588   0                                           0.1         0.126         0.569   0.03                                        0.2         0.252         0.565   0.04                                        0.3         0.378         0.570   0.03                                        0.5         0.630         0.560   0.05                                        0.6         0.756         0.561   0.05                                        0.8         1.01          0.543   0.08                                        1.0         1.26          0.528   0.10                                        1.5         1.89          0.502   0.15                                        3.5         4.41          0.438   0.26                                        4.0         5 04          0-490   0.17                                        5.0         6.30          0.415   0.29                                        6.0         7.56          0.416   0.29                                        8.0         10.08         0.336   0.43                                        15          18.9          0.223   0.62                                        20          25.2          0.168   0.71                                        30          37.8          0.131   0.78                                        ______________________________________                                    

As the UV dose delivered. to the sample film is increased there isclearly an overall increase in the conversion of the norbornene monomer.By plotting the fractional conversion against the fluence, an overallevaluation of the cure response can be made. This plot, labeled aspoly(TMO)DN, is shown in FIG. 2. A similar experiment was carried outusing the dinorbornene carboxylate ester of ethoxylated bisphenol A(EBPADN), a prior art monomer, as a replacement for the poly(TMO)dinorbornene carboxylate material, in an equivalent stoichiometriccomposition with PETMP. The results of this experiment are also shown inFIG. 2, so that a comparison of the two systems may be made. In thissecond test the UV irradiance was 1.14 mW/cm² otherwise the experimentalconditions were identical. It is unlikely that the small difference inlight intensity would result in a significant difference in photocureresponse.

The data in FIG. 2 clearly shows the advantages of the new poly(TMO)dinorbornene monomers in comparison to the prior art materials. Thephotosensitivity of these products may be defined as the minimum energyrequired to immobilize the material.

Since alkene-thiol compositions cure by a step growth mechanism, thetheoretical gel point may be predicted with some accuracy from aknowledge of the degree of functionality and the stoichiometric balanceof the two comonomers. As described in C. Macosko and D. Miller,Macromolecules, 9, (2), 199 (1976), the fractional conversion at gelpoint, α, is given by the equation: ##EQU1## where f_(a) and f_(b) arethe functionalities of the two comonomers and r is the stoichiometricimbalance defined as the ratio Na/Nb (Nb>Na), where Na and Nb are thenumber of reactive equivalents of each type of the two kinds offunctional groups present. The values of Na and Nb may be estimated asthe product of the functionality and number of moles of each comonomerpresent. If α is <1, then a crosslinked gelled polymer is predicted tobe produced at that fractional conversion. If, on the other hand, α>1,then only non-crosslinked linear and/or branched polyfunctionaloligomers are predicted to be produced. Such materials are polydisperseand polyfunctional in unreacted b groups. In the case where f_(a) andf_(b) are 2 and 4 for the diene and tetra thiol respectively and theformulation is stochiometrically balanced, i.e., r=1, the predicted gelpoint conversion occurs at a fractional conversion of 0.58. In relationto FIG. 2, where both compositions have been formulated such that r=1,it can be seen that the fluence required to gel the poly(TMO)composition is approximately 20 mJ/cm2, whereas the corresponding valuerequired to gel the EBPADN product is approximately 300 mJ/cm2. Thus thephotosensitivity of the present poly(TMO) products is 15 times greaterthan the prior art EBPADN containing compositions. This result isparticularly surprising, since the molecular weight of the poly(TMO)monomer (1278) is twice the molecular weight of EBPADN (634).

In addition the new poly(TMO) resin containing composition has the addedadvantage of giving a higher extent of polymerization than is possiblewith the existing norbornene-thiol resins as exemplified by EBPADN. Thepoly(TMO) material gives up to 80% conversion with little reduction inreaction rate and may be projected to full cure with relatively littleadditional energy. The network structure is therefore essentiallycomplete with little or no unreacted functional groups. This contributesto the mechanical performance of the cured composition, and renders theproduct less susceptible to further environmental, chemical and physicalchange. In contrast, the EBPADN has an ultimate conversion at or nearthe theoretical gel point of 58% and it can be seen from FIG. 2, thatadditional energy would not be expected to increase the conversionsignificantly. In this case the network is far from complete and a highconcentration of unreacted norbornene and thiol groups are present inthe cured structure. In this state the product is prone to furtherreaction after the initial curing stage, resulting in unpredictablechanges in physical properties. This makes the material unsuitable forsome applications, particularly for the primary coating of opticalfibers.

The above equation may also be used to define the upper limits of themolar ratio of the norbornene and thiol monomers used in the productionof the prereacted oligomer for compatabilizing the respective componentsof the compositions of the invention. Since the requirement is that theprereacted material be soluble in the unreacted norbornene, a gelledproduct must be avoided. The value of r must therefore be such that α is1 or greater. In the examples of this application, a di-functional eneand tetra-functional thiol are employed and the corresponding values off_(a) and f_(b) are therefore 2 and 4 respectively. By solving theequation for r, with α=1, the maximum stoichiometric imbalance of thesetwo comonomers that may be used to form the oligiomer may be determined,viz. 0.33. Desireably, the oligomerization reaction should be run tocomplete conversion of the less abundant monomer, i.e. the norbornenematerial.

It should be noted that maximum allowable value of r will changeaccording to the functionality of the comonomers. For example atetra-functional ene and tetra-functional thiol will crosslink if thestoichiometric imbalance exceeds 0.11; a diene and trithiol willcrosslink if the value exceeds 0.50, etc. If mixtures of different neneand thiol comonomers, having the same reactivity, are employed, then thefunctionalities f_(a) and f_(b) are replaced by the corresponding weightaveraged values.

The lower limit on the value of r is determined only by the solubilitydifficulty encountered between the polythiol and norbornene components.There must be sufficient oligomer to enhance the solubility of thecomonomers in the final formulation. Generally an oligomer formed from anorborne/thiol mixture to improve solubility should have a value of r ofat least r¹ /100 (where r¹ is the value of r when α=1) with a preferredvalue of at least r¹ /10. The preferred range of comonomerconcentrations for production of prereacted oligomers would therefore bebetween r¹ /10 and r¹.

In Example 12 the oligomer has been prepared with the thiol in excess.It is expected that a prereacted oligomer prepared with excess alkenewould provide the same benefits although the structure of the productwould be different. The same definitions as to the stoichiometry applyregardless of which monomer is in excess.

Having prepared the oligomer, the final crosslinkable composition may beformulated by addition of the appropriate quantity of the depletedmonomer along with photoinitiator and other additives. The overallstoichiometry will depend on the particular physical properties requiredof the crosslinked polymer. The value of r for the final compositionmust be selected such that α is less than 1. For the diene andtetra-thiol this translates to a value for r in excess of 0.33. Optimalproperties are usually obtained when there is an exact equivalence ofthe two types of functional groups, i.e. r=1. However it is possible andsometimes desirable to modulate the properties by changing thestoichiometry.

Trithiol Based Formulations

The manufacturing of the coated optical fiber is dependent on severalvariables, one being the speed at which the manufacturer can draw theglass fiber, but another very important variable is the UV dose at whichthe primary coating is fully cured. The lower the UV dose required forfull cure, the more the rate of manufacturing becomes almost entirely afunction of the speed of drawing the optical fiber. By having a coatingthat requires a low UV dose for substantially complete cure, themanufacturer can concentrate on the glass processing. The UV doserequired for substantially complete cure was measured by determinationof the material's tensile modulus at several UV doses, since this alsorelates to the manufacturing need for the coating to quickly establish asolid structure. In Lee, et al, U.S. Pat. No. 5,169,879, the compositionis defined as cured when the surface was tackfree and the physicalproperties near maximum (column 11, 64-66). This definition will be usedin the work presented in the following examples.

UV Curing

Sample preparation was carried out under yellow lighting to eliminateall background UV radiation. A collimated Oriel UV light source (OrielCorporation) was used for room temperature curing; this device uses adichroic mirror to remove the infrared component of the light. Lightintensity was measured with a radiometer (peak sensitivity 365 nm).Three measurements were taken before any samples were cured, and threeafter the last sample was cured. The average intensity was 22.80 mW/cm2.Shutter control within 0.1 second was possible using an Oriel electronictimer control. Although these conditions do not duplicate the curingconditions on a manufacturing line, they were chosen to show how rapidlythe material achieves tack free dose and a tensile modulus that is at ornear the maximum modulus, even at low ultraviolet intensities where noheat is provided to further promote the polymerization reaction. Manyreferences, including U.S. Pat. Nos. 5,169,879; 5,139,872 and 4,956,198refer to medium pressure Hg arc lamps, which are well known to thoseskilled in the art to emit UV radiation of much higher intensity and toemit a significant amount of heat during exposure. UV Fusion Systems, amanufacturer of a commonly used UV curing apparatus which incorporatesmedium pressure lamps, states in their "Operation and MaintenanceManual" that the surface temperatures of the lamp during normaloperation will exceed 120° F. This in fact is exactly the system used inU.S. Pat. No. 4,956,198. In contrast, the use of low intensity UVradiation, and the ability to achieve full cure at low intensities, areadvantages in terms of manufacturing set-up and maintenance costs (lowintensity lamps are less expensive and it is less costly to retrofit anassembly line with lower-intensity lamps), in terms of minimizingpossible worker hazards from exposure to stray high intensity UV beams,and also in prevention of heat exposure by and damage to sensitivecomponents (electronic and otherwise).

Thin Film Sample Testing

An Instron 4505 Universal Testing Machine interfaced with Series IXsoftware was used to measure tensile properties. This machine wasequipped with a 10N (2.25 lb) dual tension/compression load cell andpneumatic clamps with rubber-faced grips. The load cell is accurate to0.4%, or 0.041N (0.009 lb). The gage length used was 5.0 cm (1.97 in),and the crosshead speed was 2.5 cm/min (0.98 in/min). Tensile propertiesgiven in the examples are the average of 5°-8 samples.

Glass transition temperature was obtained via dynamic mechanicalanalysis using a Rheometrics Dynamic Analyzer in the rectangular torsionmode. The range of strain at which the material's linear elastic region[LER] existed was first determined by several strain sweeps with thematerial at a temperature where it was in its glassy phase. Then, virginmaterial was used in a temperature sweep where the strain applied waswithin the material's LER, and the glass transition temperature (Tg) wastaken as the temperature corresponding to the maximum in the tan δ peak.Values given for Tg are the average of two to three measurements, allmade on virgin samples.

ASTM D-542 was used to obtain the refractive index, and a modifiedversion of ASTM D-570 was used to obtain both water absorption and waterextractibles. All numbers are the averages of three to fourmeasurements.

Examples 14-17 serve the purpose of illustrating the glass transitiontemperature, refractive index, water absorption and speed ofpolymerization of formulations using trithiols. The trifunctional thiolused in these examples, trimethylolpropane trimercaptopropionate([TMP]2), is immediately miscible in poly(tetramethylene oxide 1000)dinorbornene carboxylate [p(TMO 1000)DN], in a range of proportions, anda stoichiometric formulation has a viscosity between 500-800 cps[500-800 mPas]. The details of each formulation are given below.

EXAMPLE 14

1.0:1.0Nene/thiol ratio formulation

36.25 g [TMP]2

162.7 g p(TMO 1000)DN

4.0 g DAROCUR 1173

0.2 g Q1301

0.1 gBHT

0.1 g MEHQ

This formulation cured to tack-free films at a dose of 101.2 mJ/cm² withan average thickness of 9.3 mils (0.023 cm). At that dose, the tensilemodulus was 313 psi [2.16 MPa], tensile strength was 134.6 psi [0.93MPa] and elongation at break was 73.3%. At a dose of 303.8 mJ/cm²,average film thickness was 9.4 mils (0.024 cm) and the tensile moduluswas 316.1 psi [2.18 MPa], with a tensile strength of 111 psi [0.76 MPa]and an elongation to break of 53.0%. At a dose of ˜987.2 mJ/cm², withaverage film thickness of 10.3 mils (0.026 cm) the modulus was 397 psi[2.74 MPa], tensile strength was 112 psi [0.76 MPa] and elongation atbreak was 43.4%. The glass transition temperature of this material wasfound to be - 50.65° C. The index of refraction (nD) of the liquid wasfound to be 1.4841 at 25° C. Water absorption after 24 hours at roomtemperature was found to be 0.78% and extractibles were found to be2.51%.

EXAMPLE 15

1.0:1.25Nene/thiol ratio formulation

43.33 g [TMP]2

155.56 g p(TMO 1000)DN

4.0 g DAROCUR 1173

0.2 g Q1301

0.1 g BHT

0.1 g MEHQ

When irradiated at a dose of 99.4 mJ/cm², tack-free films of averagethickness 9.2 mils (0.023 cm) were produced with tensile modulus of107.8 psi [0.74 MPa], tensile strength of 66.8 psi [0.46 MPa], andelongation at break of 125%. When the formulation was irradiated at300.5 mJ/cm², films of average thickness 8.5 mils (0.022 cm), thetensile modulus was 128 psi [0.88 MPa], the tensile strength was 68 psi[0.47 MPa] and the elongation at break was 101%. At a dose of 987mJ/cm², the films had an average thickness of 8.5 mils (0.022 cm) withmodulus of 143.1 psi [0.99 MPa], tensile strength of 81 psi [0.56 MPa]and elongation at break of 109%.

EXAMPLE 16

1.0:1.0Nene/thiol ratio formulation with 4-acetoxystyrene

36.25 g [TMP]2

162.7 g p(TMO 1000)DN

4.0 g DAROCUR 1173

0.2 g Q1301

0.1 gBHT

0.1 g MEHQ

0.8 g 4-acetoxystyrene

When this formulation was irradiated at a dose of 296.4 mJ/cm²,tack-free films of average thickness 10.8 mils (0.027 cm) were producedwith tensile modulus of 386 psi [2.66 MPa], tensile strength of 130 psi[0.90 MPa] and elongation at break of 55%. When irradiated at a dose of987.2 mJ/cm², films had an average thickness of 10.6 mils (0.027 cm)with modulus of 407 psi [2.81 MPa], tensile strength of 161 psi [[1.11MPa], and elongation at break of 68%. Water absorption after 24 hours atroom temperature was found to be 0.56% and extractibles were found to be3.15%.

EXAMPLE 17

1.0:1.25Nene/thiol ratio formulation with 4-acetoxystyrene

3.33 g [TMP]2

155.56 g p(TMO 1000)DN

4.0 g DAROCUR 1173

0.2 g Q1301

0.1 gBHT

0.1 g MEHQ

0.8 g 4-acetoxystyrene

After irradiation of the formulation at a dose of 298 mJ/cm², tack-freefilms were produced having average thickness of 12.3 mils (0.031 cm)with tensile modulus of 118.3 psi [0.82 MPa], tensile strength of 66.5psi [0.46 MPa] and elongation at break of 116%. After irradiation of theformulation at a dose of 992 mJ/cm², films of average thickness 11.0mils (0.028 cm) had tensile modulus of 138 psi [0.95 MPa], tensilestrength of 61 psi [0.42 MPa] and elongation at break of 77%

Thiol Prepolymer Formulations

Examples 18-21 serve the purpose of illustrating the glass transitiontemperature, refractive index, water absorption and speed ofpolymerization of formulations using a tetrathiol propolymer. Thetetrafunctional thiol used in these examples was prepared by combining301.2 g p(TMO 1000)DN, 205.0 grams PETMP in a 950 ml widemouth amberglass bottle. The mixture was heated to 85° C. while stirred for 4hours. After 4 hours, the extent of conversion was checked via IR andbeing acceptable, the bottle was capped and refrigerated.

All of the following samples were prepared by adding the necessaryamount of norbornene (p(TMO 1000)DN) to a known amount of prepolymer inorder to obtain either 1:1 stoichiometry (nene/thiol) or 1:1.25nene/thiol stoichiometry. p(TMO 1000)DN was added to the prepolymer, andwas mixed with an air motor until miscible (checked visually--nocloudiness, no interface between the two components). Then a premixcontaining photoinitiator (DAROCUR 1173, 2 wt %), Q1301 and for examples19 and 21, 2-propenylphenol (Aldrich) was added and further stirred. Theonset of oxidation was measured using a Perkin Elmer TGA; tests were runin air at a scan rate of 5° C./min, with sample size between 2.2-3.2 mg.Formulations and properties obtained are shown below:

    __________________________________________________________________________                 Example 18                                                                           Example 19                                                                           Example 20                                                                           Example 21                                  __________________________________________________________________________    Material                                                                      Polythiol prepolymer                                                                       138.6 g                                                                              166.0 g                                                                              138.6 g                                                                              166.0 g                                     p(TMO 1000)DN                                                                              191.4 g                                                                              163.9 g                                                                              191.4 g                                                                              163.9 g                                     Q1301        1000 ppm                                                                             1000 ppm                                                                             250 ppm                                                                              250 ppm                                     2-propenyl phenol                                                                          0 ppm  0 ppm  4000 ppm                                                                             4000 ppm                                    Stoichiometry,                                                                             1.0:1.0                                                                              1.0:1.25                                                                             1.0:1.0                                                                              1.0:1.25                                    nene:thiol                                                                    Properties                                                                    Tg, °C.                                                                             -50.3  -50.3  -50.3  -50.6                                       Refractive                                                                    Index, Liquid                                                                              1.4875 1.4894 1.4868 1.4892                                      Water                                                                         Absorption, %                                                                              0.86   0.78   0.79   0.80                                        Water                                                                         Extractibles, %                                                                            0.68   0.68   0.79   0.62                                        Film cured at 100 mJ/cm.sup.2 :                                               Tensile Modulus, psi                                                                       540 + 28                                                                             364 + 18                                                                             515 + 22                                                                             371 + 28                                    [MPa]        [3.72 + 0.19]                                                                        [2.51 + 0.12]                                                                        [3.55 + 0.15]                                                                        [2.55 + 0.19]                               Elongation at                                                                              30.4 + 12.6                                                                          49.7 i 18.3                                                                          36.4 + 17.4                                                                          53.0 + 12.1                                 Break, %                                                                      Film cured at 300 mJ/cm.sup.2 :                                               Tensile Modulus, psi                                                                       538 + 28                                                                             369 + 3                                                                              527 +  19                                                                            384 + 11                                    [MPa]        [3.70 + 0.19]                                                                        [2.54 + 0.02]                                                                        [3.63 + 0.12]                                                                        [2.65 + 0.08]                               Elongation at                                                                              20.5 + 3.3                                                                           35.4 + 7.4                                                                           19.6 + 4.5                                                                           32.0 + 8.4                                  Break, %                                                                      Onset of oxidation,                                                                        268.6  258.8  267.8  270.8                                       °C.                                                                    __________________________________________________________________________

Since water absorption can adversely affect static fatigue and opticalproperties of optical fibers, a low degree of water absorption isconsidered very desirable for optical fiber coating materials. The waterabsorbtion of these formulations is excellent compared to prior artmaterials and the water extractables comparable to previously reportedmaterials. See, for instance, U.S. Pat. No. 4,956,198; Chander P. Chawlaand James M. Julian, "An Infrared Study of Water Absorption of UVCurable Optical Fiber Coatings", RadTech Report, January/February 1992,p.2428; and Jan Martin, "Contribution of Dual UV Cured Coatings toOptical Fiber Strength and Durability," (De Soto, Inc.), Radcure Europe'87, p.4-15.

EXAMPLE 22

A formulation was prepared as follows:

    ______________________________________                                        Material         Amount, kg                                                   ______________________________________                                        pTMO(1000)DN     12.11                                                        Treated [TMP]2   2.7                                                          LUCERIN TPO.sup.1                                                                              0.111                                                        Acetoxystyrene   0.06                                                         BHT              0-0075                                                       MEHQ             0.0075                                                       Q1301            0.0015                                                       ______________________________________                                         .sup.1 Photoinitiator sold by BASF                                       

PTMO(1000)DN was charged into reactor and stirred with nitrogen blanket.In a glass flask with nitrogen the treated (slurried with Magnesol andthen filtered) [TMP]2 was mixed with Lucerin TPO until dissolved.Meanwhile, in a glass beaker with a magnet stirrer a premix of4-acetoxystyrene, MEHQ, BHT and Q1301 were mixed until dissolved. Thismixture was then added to the flask containing the thiol/Lucerin TPOsolution and the resulting combination was stirred for 10 minutes. Afterthat time the solution was added to the reactor, and all components ofthe formulation were mixed under nitrogen for 15 minutes. Theformulation was then filtered through a 3-micron filter into anarrow-necked brown bottle.

EXAMPLE 23

A polythiol prepolymer was synthesized by combining 4.84 kg p(TMO1000)DN and 3.3 kg PETMP which were mixed at 80° C. until full reactionhad occurred. This was monitored via IR and required roughly 11/2working days for full reaction. The mixture was then cooled to 25° C.and flushed with nitrogen. Once the temperature had stabilized at 25°C., a stabilizer solution of 4-acetoxystyrene (0.079 kg), Q-1301 (0.002kg), BHT (0.0119 kg) and MEHQ (0.0079 kg) was added. Additional (11.2kg) unreacted pTHF(1000)DN was added to bring the stoichiometry to1.0:1.0 nene/thiol. This combination was then mixed for 25 minutes.DAROCUR 1173 was then added (0.572 kg) and mixing continued for 1 hour.The formulation was then filtered through a 25 micron bag into brownjugs.

EXAMPLE 24

Optical fiber which had been coated with either p(TMO 1000)DN/PETMP(Example 24) or p(TMO 1000)DN/[TMP]2 (Example 23) and a commercialsecondary coating was tested. Properties studied included thetemperature dependence of change in decibel per kilometer of fiber(dependence of attenuation on temperature), strip force, waterabsorption and water extractibles, and pullout force. Test methods usedare well-known to those familiar with the art of manufacturing opticalfibers. Properties are listed below.

    ______________________________________                                                   Fiber Coated                                                                             Fiber Coated                                                                             Bellcore TR-20,                                         with       with       issue 5                                      Property   Example 23 Example 24 specification                                ______________________________________                                        Temperature                                                                   dependence                                                                    δdB/km                                                                  (@1300/1550 nm)                                                               at -40° C.                                                                        0.0/0.0    0.0/0.0    <0.05                                        at -60° C.                                                                        0.0/0.0    0.0/0.0    <0.05                                        Strip Force (lb.sub.f),                                                                  0.75       0.78       >0.3, <2.0                                   dry                                                                           Water      0.62       0.64                                                    Absorption, %                                                                 Water      0.33       0.27                                                    Extractibles, %                                                               Pullout Force                                                                            1.31       1.23                                                    (lb.sub.f) 50% RH                                                             ______________________________________                                    

What is claimed is:
 1. A curable thiol-ene composition comprising apolythiol and a compound having a plurality of norbornene groupsthereon, whereinthe compound having the plurality of norbornene groupsor the polythiol has a backbone consisting of a poly(tetramethyleneoxide), or the compound having the plurality of norbornene groups or thepolythiol is an oligomer of a parent compound having a plurality ofnorbornene groups and a backbone consisting of a poly(tetramethyleneoxide) or is an oligomer of a parent polythiol having a backboneconsisting of a poly(tetramethylene oxide),and the poly(tetramethyleneoxide) has a molecular weight of between 250 and 5,000.
 2. A compositionas in claim 1 further comprising a free radical photoinitiator.
 3. Acomposition as in claim 1 wherein the compound having the plurality ofnorbornene groups thereon is a norbornene terminated poly(tetramethyleneoxide) or a norbornene functional oligomer of a said norborneneterminated poly(tetramethylene oxide) and a polythiol.
 4. A compositionas in claim 3 wherein the ratio of norbornene to thiol groups is between1.0:0.8 and 1.0:1.3.
 5. A composition as in claim 3 wherein thenorbornene terminated poly(tetramethylene oxide) is selected from thegroup consisting of: ##STR6## wherein n is an integer of 1-30.
 6. Acomposition as in claim 3 wherein the polythiol of said composition isfully miscible with the plural norbornene compound.
 7. A crosslinkedpolymer produced by curing a composition as in claim
 3. 8. A polymer asin claim 7 having a Tg of -20° C. or less.
 9. A polymer as in claim 8having a Tg of -35° C. or less.
 10. A polymer as in claim 9 having a Tgof -50° C. or less.
 11. A polymer as in claim 7 having a modulus of lessthan 800 psi (5.52 MPa).
 12. A polymer as in claim 7 having a degree ofwater absorption of less than 1.0%.
 13. A composition as in claim 1wherein the polythiol of said composition is a thiol functional oligomerof a norbornene terminated poly(tetramethylene oxide) and astoichiometric excess of a compound having at least three thiol groupsthereon.
 14. A composition as in claim 1 wherein the polythiol of thecomposition is a thiol functional oligomer formed from a mixture ofnorbornene and thiol functional compounds, the mixture having a valuefor r in the equation: ##EQU2## of between r¹ and r¹ /10, where α is thefractional conversion at the gel point, f_(a) and f_(b) are the weightaverage functionalities of the norbornene and thiol compound components,respectively, r is the stoichiometric imbalance defined as the ratioNa/Nb, where Na and Nb are, respectively, the number of equivalents ofnorbornene and thiol groups present and r¹ is the value calculated for rwhen α=1.
 15. A composition as in claim 1 which is a liquid having aviscosity of no more than 10,000 mPas at 60° C.
 16. A composition as inclaim 9 which is a liquid having a viscosity of no more than 2,000 mPasat 25° C.
 17. A composition as in claim 1 wherein the molecular weightof the poly(tetramethylene oxide) is 650-1000, as determined by hydroxylnumber.
 18. A composition as in claim 1 wherein the polythiol of thecomposition is selected from the group consisting of trimethylolethanetris-mercaptopropionate, trimethylolpropane tris-mercaptopropionate,trimethylolethane tris-mercaptoacetate, trimethylolpropanetris-mercaptoacetate, pentaerythritol tetramercaptoacetate,pentaerythritol tetrakis-β-mercaptopropionate and oligomers thereof witha norbornene terminated poly(tetramethylene oxide).
 19. A composition asin claim 1 further comprising an adhesion promoter.
 20. A composition asin claim 19 wherein the adhesion promoter is selected from the groupconsisting of acrylic and norbornene acid phosphate esters; itaconic,acrylic and methacrylic acids; maleic, fumaric and norbornenedicarboxylic acids and their half esters; and thiol, epoxy, norbornene,acrylic or methacrylic functional silane compounds having two or threehydrolyzable groups bound to silicon.
 21. A composition as in claim 20wherein the adhesion promoter is selected from the group consisting of3-methacryloxypropyl trimethoxysilane, mercaptopropyl trimethoxysilane,and glycidoxypropyl trimethoxysilane and is present in the compositionat a level of 0.1-3.0 percent by weight.
 22. A crosslinked polymerproduced by curing a composition as in claim 1.